N-methyl ortho-bipyridines as a new member of metal-free electrocatalysts for hydrogen evolution reaction (HER): The influence of the substituent on a heteroatom on the pathway (mechanism) HER

Abstract

Using the method of cyclic voltammetry (CV), the electrocatalytic activity in the hydrogen evolution reaction (HER) in the presence of perchloric acid and N-methyl-2,2′-bipyridinium and N,N′-dimethyl-2,2′-bipyridinium iodides was studied. Conducting preparative electrolysis with simultaneous gas chromatography showed that in both cases the catalytic process is realized, however, in the case of N,N′-dimethyl-2,2′-bipyridinium iodide, the efficiency of the electrocatalytic process is much higher than in the case of N-methyl-2,2′-bipyridinium iodide. It has been shown for the first time the possibility to selectively engage different catalytic centers to hydrogen evolution reaction by varying the potential or the concentration of the acid. So, in case of N,N′-dimethyl-2,2′-bipyridinium iodide at low acid concentrations the catalytic process proceeds according to a homogeneous mechanism in parallel on both catalytic centers. At high acid concentrations on the CV two new waves appear which associated with the formation of additional pathways for the generating of molecular hydrogen - in the second wave it is realized according to the intramolecular mechanism, while in the third wave it is realized according to the heterogeneous mechanism. In the case of N-methyl-2,2′-bipyridinium iodide, one catalytic center can be selectively involved or both centers can “work” in parallel according to a different mechanism by varying the potential of the electrocatalytic process. It is important to note that the discovered phenomenon has not been previously described in the literature.